At 100°C and 1 atm if the density of the liquid water is 1.0 g cm-3 and that of water vapour is 0.0006 g cm-3, then the volume occupied by water molecules in 1 L of steam at this temperature is
a. 6 cm3
b. 60 cm3
c. 0.6 cm3
d. 0.06 cm3